1. Field of the Invention
The present invention relates to a conveyor system used in conjunction with an unloading apparatus to transfer pulverized or comminuted materials from relatively large cargo containers or vessels to a material transport, handling or storage system. More particularly, this invention relates to a conveyor system used in conjunction with an unloading apparatus to transfer dry cement or other loose, powdered material from the unloading apparatus to a material transport, handling or storage system.
The transfer of various comminuted materials presents difficult problems; however, cement, because of its physical properties, is particularly troublesome. Dry cement is a fine powdered material, 100 mesh or under in size. It is mildly abrasive, and it flows relatively freely at an angle of repose of 30.degree. to 45.degree.. When aerated it becomes fluid-like, but when packed or settled, it becomes dense and difficult to handle. It is well known that cement has strong adhesive properties when combined with water, and it deteriorates drastically when exposed to moisture. Once properly mixed, it sets and hardens very quickly.
When the cement is in its fluffy, aerated condition, it poses unique handling and transport problems. If the container used to hold the cement or the system used to transport it are open to the elements, the wind blows away the dust-like particles of cement. In addition to the loss of the product, cement particles in the air present a number of problems. They create a harsh environment which accelerates the wear of equipment and creates a health hazard to people who must work in this environment.
If the containers or transport system are open to moisture, the cement will combine with the water, set and quickly harden into a solid mass. Because of the cement's strong adhesive properties, this mass may adhere to the equipment, resulting in wear or failure of the equipment and in undesirable and expensive downtime. Cement which has combined with water and set is waste material requiring disposal. The cost of lost material and disposal is also an undesirable expense. A material handling system, including a conveyor, must be capable of handling the cement while preventing the cement from damaging the equipment, and it must be capable of maintaining the cement in a stable condition.
2. Description of the Prior Art
Pneumatic systems have been used to move small quantities of cement. However, these pneumatic systems use positive pressures to move the cement. In using positive pressures, the systems require excessive power and expensive equipment for air-cement separation. Accordingly, these systems have proven inefficient or ineffective for larger quantities. Thus, organizations which move large quantities of cement, such as the manufacturers of the cement, have relied upon several different types of mechanical systems.
One known type of mechanical system uses scrapers, feeders and enclosed vertical conveyors to remove cement from barges and other material containers and place it on a transport system which takes it to another material handling or storage system. The transport system most commonly used is a horizontal conveyor. Unhoused horizontal conveyor systems have been used, but these devices expose the cement to wind, rain, and snow and encounter the problems discussed above. Totally enclosed horizontal conveyor systems have also been used; but with these systems the apparatus can only deposit the cement at a limited number of points along the conveyor. Most of these systems also require that the barge or container move during the unloading because of the limited number of entry points. In addition, since the conveyor mechanism is totally enclosed, when the system breaks down the resulting downtime is long due to the difficulty of gaining access to the conveyor mechanism.